The plant has no stems, leaves or roots. It is a holoparasite of vines in the genus Tetrastigma, spreading its absorptive organ, the haustorium, inside the tissue of the vine. The only part of the plant that can be seen outside the host vine is the five-petalled flower. In some species, such as Rafflesia arnoldii, the flower may be over in diameter, and weigh up to. A Rafflesia that flowered in West Sumatra in 2019 was measured to be almost in diameter, the largest flower ever recorded – wider than the flower reported as the largest in 2017. Even one of the smallest species, R. baletei, has diameter flowers. The flowers look and smell like rotting flesh, hence its local names which translate to "corpse flower" or "meat flower". The foul odor attracts insects such as flies, which transport pollen from male to female flowers. Most species have separate male and female flowers, but a few have hermaphroditic flowers. Little is known about seed dispersal. However, tree shrews and other forest mammals eat the fruits and disperse the seeds. Rafflesia is the official state flower of Indonesia, where it is known as puspa langka or padma paksasa, of Sabah state in Malaysia, and of Surat Thani Province in Thailand. In Thailand, Rafflesia can be observed in Khao Sok National Park where the flowers are numbered and monitored by the park rangers. Rafflesia are also remarkable for showing a large horizontal transfer of genes from their host plants. This is well known among bacteria, but not higher organisms.
Name
The name "corpse flower" applied to Rafflesia can be confusing because this common name also refers to the titan arum of the family Araceae. Moreover, because Amorphophallus has the world's largest unbranched inflorescence, it is sometimes mistakenly credited as having the world's largest flower. Both Rafflesia and Amorphophallus are flowering plants, but they are only distantly related. Rafflesia arnoldii has the largest single flower of any flowering plant, at least in terms of weight. Amorphophallus titanum has the largest unbranched inflorescence, while the talipot palm forms the largest branched inflorescence, containing thousands of flowers; the talipot is monocarpic, meaning the individual plants die after flowering. The flower is sometimes called the "monster flower" for its parasitic tendencies and foul odor.
Classification
Comparison of mitochondrial DNA sequences of Rafflesia with other angiosperm mtDNA indicated this parasite evolved from photosynthetic plants of the order Malpighiales. Another study from that same year confirmed this result using both mtDNA and nuclear DNA sequences, and showed the three other groups traditionally classified in Rafflesiaceae were unrelated. A more recent study more specifically found Rafflesia and its relatives to be embedded within the family Euphorbiaceae, which is surprising, as members of that family typically have very small flowers. According to their analysis, the rate of flower size evolution was more or less constant throughout the family except at the origin of Rafflesiaceae, where the flowers rapidly evolved to become much larger before reverting to the slower rate of change.
Species native to Borneo include Rafflesia arnoldii, Rafflesia cantleyi, Rafflesia hasseltii, Rafflesia keithii, Rafflesia kerrii, Rafflesia pricei, and Rafflesia tengku-adlinii. R. arnoldii boasts the world's largest single bloom. Some endemic Borneon species, such as R. keithii, begin blooming at night and start to decompose only two to three days later. The time from bud emergence to flowering is six to nine months. Male and female flowers must be open simultaneously for pollination to occur, hence successful pollination and fruit production are quite rare. In addition to habitat loss, these reproductive limitations are contributing factors to why many species are endangered. R. keithii is found along the eastern slopes of Mount Kinabalu in the Lohan Valley of Sabah. Rafflesia tuan-mudae is endemic to only Gunung Gading National Park in Sarawak.
The Mindanao species is known as Rafflesia schadenbergiana, after the naturalist Alexander Schadenberg, who first discovered the species at the foothills of Mount Apo in 1882. With a flower of nearly a meter, it is close to the size of a 7 year old child when seated. On Mindanao, the species has been seen in Davao del Sur, South Cotabato and Mount Kitanglad in Bukidnon. Second, Rafflesia mira and Rafflesia magnifica are two names for a single species. Both were discovered at Mount Candalaga in Maragusan, Compostela Valley. The two forms differ in size measurements in which the scientific description of Magnifica came from measurements of flowers in full bloom while that of Mira was from photographs of nearly dead samples. The medium-sized Mira and Magnifica flowers measure about half a meter and they have round or elliptic perigone wart. The third species on Mindanao is the Rafflesia mixta which is found so far only in the town of Mainit, Surigao del Norte. It shows a combination of three features of Philippine Rafflesia, namely: the shape and size of the conical process in Rafflesia schadenbergiana, the floral size and sparsely distributed perigone warts of R. speciosa, and the overall resemblance, floral size, faint scent, diaphragm and ramenta morphology of R. mira. Fourth, is Rafflesia verrucosa which is found only in Mount Kampalili in Davao Oriental Province.
Research published in the journal Molecular Biology and Evolution revealed that one Philippine Rafflesia species from the island of Luzon, Rafflesia lagascae, has lost the genome of its chloroplast and it is speculated that the loss happened due to the parasitic lifestyle of the plant.
